Abstract

People perceive smooth luminance variations as being due to the shading produced by surface undulations: shape-from-shading. To do this the visual system must simultaneously estimate the nature of the illumination and the shape of the surface. Shape-from- shading operates even when both these properties are unknown and neither can be estimated directly from the image. In such circumstances humans are thought to adopt a default illumination model. It is widely held that the default illuminant is a point source located above the observer’s head, but some have argued that the default illuminant is a diffuse source. We present evidence that humans adopt an illumination model that includes both diffuse and directional (overhead) elements.